Catheters are commonly used for enteral feeding, urinary bladder drainage and irrigation, suctioning of blood and mucous, as well as for other purposes in the medical treatment of humans. Exemplary catheters are illustrated and described in U.S. Pat. Nos. 4,594,074, 4,410,320, 4,390,017, 4,388,076, and 4,220,542. Each of these catheters employs a tube with a distal end opening, either axially through the tube end or through its side.
In the type of catheter illustrated in U.S. Pat. No. 4,594,074, the distal end of the catheter tube is provided with a tip or bolus, as it is called, in which a side opening is formed. The bolus has a generally cylindrical passage in it with an internal diameter corresponding to the internal diameter of the tube on which it is mounted. The bolus opening or port is formed through its side wall and the side wall, on each side of the opening, is generally vertical, i.e., those side wall portions bracketing the opening extend parallel to each other. This configuration produces a bolus in which the side wall, at the opening, encloses at least 180.degree. of the inside circumference of the passage in the bolus. In addition to having a bolus opening or port of the aforedescribed nature and configuration, the floor of the passage below the port curves upwardly on an arc of substantial radius. The result attributed to this bolus design is a fluid flow characteristic which substantially approximates the fluid flow characteristics of an open-ended tube, yet does not become occluded with mucous or feeding material.
The tube and bolus designs illustrated and described in the aforementioned patents, including U.S. Pat. No. 4,594,074, all have at least one drawback, however. When used in an aspiration mode in the stomach or bladder, for example, the bolus opening or port may become clogged, either by mucosa in the stomach or the wall of the bladder. This is true notwithstanding the fact that the very purpose of the bolus design in the '074 patent, for example, is to avoid such malfunctions, because the port can be bridged too easily transversely of the bolus by the occluding surface.